Handy pin-out diagram for the pre-OBD 20-pin round diagnostic connector on 80s
and 90s BMWs from PinOutGuides.com
[https://pinoutguide.com/CarElectronics/car_diag_pinout.shtml]
1 Engine rotation speed [TD]
2 CAN-High
3 CAN-Low
4 Shielding
7 Oil service and Inspection reset
11 External starter turn on
12 Battery indicator
14 Battery power +12V
15 ISO 9141-2 L Line
16 Ignition +12V
17 ISO 9141-2 K Line
18 Programming line [PGSP]
19 Ground [GND]
20 ISO 9141-2 K Line [TXD]
https://pinoutguide.com/CarElectronics/car_diag_pinout.shtml